**First, Power over Ethernet Technology**
Power over Ethernet (PoE) is a technology that allows both data and power to be transmitted over standard Ethernet cables. It enables the delivery of direct current (DC) power to network devices such as IP phones, wireless access points, and surveillance cameras, while simultaneously carrying data signals. This integration simplifies installation by eliminating the need for separate power lines, making it more efficient and cost-effective. PoE relies on existing network infrastructure, ensuring safety and reliability in structured cabling systems. The IEEE 802.3af standard defines the basic PoE protocol, which allows for power delivery up to 15.4 watts. It is primarily a power delivery protocol rather than a data transmission protocol, and it has significantly expanded the applications of Ethernet beyond traditional networking.
**Second, the Structure and Principle of an Ethernet Power Supply System**
A complete PoE system consists of two main components: the Power Sourcing Equipment (PSE) and the Powered Device (PD). The PSE is responsible for supplying power to the Ethernet cable and managing the power distribution. The PD, on the other hand, is the device that receives the power, such as an IP phone or a wireless access point.
The PoE process begins when the PD detects the presence of a PSE. This is done by measuring the resistance between the two signal lines. A valid PD typically presents a 25 kΩ common-mode resistance, which helps the PSE identify it as a compatible device. Once detected, the PSE performs a second measurement to determine the power requirements of the PD. Based on this information, the PSE can safely supply the necessary power without damaging non-compliant devices. This ensures optimal use of available power resources.
There are two primary methods of power delivery in PoE: Endspan and Midspan. An Endspan PSE is integrated into the network switch or router, allowing it to provide power through the same Ethernet cable used for data transmission. In this setup, power is delivered over the same pairs used for data, typically pins 1, 2, 3, and 6 in a twisted-pair cable. This method supports various network speeds, including 10BASE-T, 100BASE-TX, and 1000BASE-T.
On the other hand, a Midspan PSE is a separate device placed between the switch and the PD. It provides power without interfering with the data signal. Midspan PSEs usually have two RJ45 ports per connection—one connected to the switch and the other to the PD. They do not use all the wires in the Ethernet cable for power delivery, instead using the spare pairs. Midspan PSEs typically support 10BASE-T and 100BASE-TX but are not yet standardized for 1000BASE-T networks. They deliver 48V DC power between the unused wire pairs, ensuring that the data flow remains unaffected.
Overall, PoE has revolutionized the way we power networked devices, offering a reliable, flexible, and efficient solution for modern communication systems.
Jiangmen Hongli Energy Co.ltd , https://www.honglienergy.com